For CPU only projects, Intel CPUs make up 94% of CPUs, AMD 4.5%, and ARM 1.3%. (and people complain of ASIC manufacture centralisation)
https://steemit.com/boinc/@nexusprime/boinc-hardware-surveyAlthough I think that ARM is more energy efficient because the processor have many optimisations for mobile computing in other to save battery life.
But BOINC have a fewer projects for RISC architecture